INSIDIOUS Synonyms: 100 Similar and Opposite Words

insidious

adjective

Definition of insidious

as in treacherous

formal causing harm in a way that is gradual or not easily noticed Most people with this insidious disease have no idea that they are infected. an insidious enemy

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Example Sentences

Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.

Recent Examples of insidious Speaking of pop music, while the new ad format is expected to have its critics, there’s a far more insidious change afoot in that Green and Pleasant Land. — Anthony Crupi, Sportico.com, 12 June 2026 But most of its failures are subtler, more insidious. — Katy Waldman, New Yorker, 10 June 2026 What makes this deal particularly insidious is the trade-off at its core. — Joe Wilkins, Futurism, 10 June 2026 Best known for comedy series like Community (2009-15) and GLOW (2017-19), Alison Brie is taking on the role of Evil-Lyn, an insidious enchantress who serves as Skeletor’s main accomplice. — Keith Langston, PEOPLE, 6 June 2026 See All Example Sentences for insidious

Recent Examples of Synonyms for insidious

Adjective

Currently, ocean data are gathered using massive research vessels that cannot safely navigate treacherous shallow reefs or breaking ice.

— Mrigakshi Dixit, Interesting Engineering, 9 July 2026
Projecting forward four years in this game is always treacherous, more so now than following the 2022 World Cup.

— Tom Bogert, New York Times, 9 July 2026

Definition of treacherous

Adjective

Messi’s longevity is a story of enduring brilliance but also subtle evolution.

— Charlotte Harpur, New York Times, 10 July 2026
Buyers will be able to tailor the interior with exclusive leather, Alcantara, and a choice of Comfort or Racing seats, both featuring six vertical grooves as a subtle nod to the six-speed layout.

— New Atlas, New Atlas, 10 July 2026

Definition of subtle

Adjective

An infusion of false hope, however, is all the equalizer was.

— Tom Krasovic, San Diego Union-Tribune, 8 July 2026
Her post received 22,000 likes, and Elon Musk—who regularly boosts white-supremacist perspectives—and Joe Rogan have made similar claims about the group being a false-flag operation.

— Ali Breland, The Atlantic, 8 July 2026

Definition of false

Adjective

The state agency said clinic staffers had clients sign a personal injury waiver, which the commission said was unenforceable, against public policy and deceptive and dishonest.

— Ashley Hiruko, ProPublica, 8 July 2026
Bartůňková and Krejčíková share finesse in the front of the court as well as deceptive power, with Bartůňková’s excellent spot-serving giving her a platform and Krejčíková’s ability to change rhythm at will trying to destabilize it.

— Ava Wallace, New York Times, 2 July 2026

Definition of deceptive

Adjective

In 2024, Air Canada's AI agent gave a passenger incorrect information about bereavement fares.

— Stu Sjouwerman, Forbes.com, 7 July 2026
Even though talks with the Boston Red Sox at last year’s deadline never got close, the confusion provided by an incorrect tweet announcing Ryan’s trade to New England put the pitcher at the top of every trade list before the season even began.

— Dan Hayes, New York Times, 6 July 2026

Definition of incorrect

Adjective

Under rules brought in for the World Cup, the reviewable decisions and incidents now include mistaken identity when the referee shows a yellow or red card but clearly penalises the wrong player of either team.

— Stuart James, New York Times, 12 July 2026
Even when Romanzy goes off on how stupid and ugly Caleb is — and gossips that his parents abandoned him because something must be wrong with him — Mary goes along with it.

— Maggie Fremont, Vulture, 11 July 2026

Definition of wrong

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inside tracks

insidious

insidiously

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Style

“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 14 Jul. 2026.

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Synonyms of insidious

adjective

Example Sentences

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